This invention concerns an automatic system for connection of pneumatic and hydraulic hoses on composite electrodes for arc furnaces.
To be more exact, the automatic connection system according to the invention is employed for the connection of the hoses conveying cooling and actuation fluids to the cooled adapter element on electrodes of a composite type used in electric arc furnaces.
The invention is used both in electric arc furnaces fed with direct current and those fed with alternating current.
The system according to the invention assists, accelerates and automates the operations of connection/disconnection of the hydraulic and pneumatic hoses during the steps of removal and replacement of the electrodes.
Moreover, the system according to the invention does not cause any impediment to the vertical movement of the electrodes during the operational steps of the furnace in that, at least during these operational steps, the connection assembly of the hydraulic and pneumatic hoses is integrated with the electrode and moves vertically with the same.
The state of the art includes composite electrodes formed with a hollow cylindrical adapter made of a metallic material and secured to the respective electrode-holder arm; to the lower end of the adapter element is fixed a consumable cylindrical graphite element from which the electric arc strikes.
The electrode of a composite type provides various advantages as compared to those made entirely of graphite; the adapter in a furnace fed with direct current may have the function of an auxiliary reactor, thus reducing the size and complexity of the external reactors normally used in the plant that supplies such furnaces.
The adapter, appropriately dimensioned, in a furnace fed with alternating current enables the currents circulating in the three phases to be balanced, thus reducing the drawbacks of the state of the art arising from an unbalanced system.
A further advantage provided by the use of composite electrodes is that they may not require previous processing for adaptation of the graphite element, for such processing is necessary, instead, for electrodes made completely of graphite; the reason for this is that the electrode is supported by the electrode-holder arm at the adapter and not at the graphite element.
The lack of previous processing makes possible a great saving of material, costs and processing times.
On the other hand, such composite electrodes require a system for cooling the adapter so as to prevent the latter being capable of being damaged owing to the high temperature of the furnace.
The cooling of the adapter is normally carried out by circulating within it a cooling fluid, normally air or water, which is fed through external hoses.
According to the state of the art these hoses are free and flexible and are secured at one end to the upper part of the adapter.
However, it is known that the electrodes during the working cycle have to be able to slide axially in relation to the electrode-holder arm so as to adjust the height of the electrodes in relation to the bath of molten metal according to the wear of the graphite segment and also have to be capable of being readily dismantled quickly so as to make possible the normal operations of maintenance and replacement of the graphite segment.
The cooling hoses form a great hindrance as they have to be disconnected to perform the operations of removal of the electrode.
In fact, while the adjustment of the axial position of the electrode is possible, the dismantling of the electrode is especially difficult since the disconnection of the hoses has to be carried out by hand.
Moreover, to perform that operation, the machine operator has to clamber onto the electrode-holder arm and thus exposes himself to the risk of accidents and contravenes the specific safety rules in force.
So as to avoid this problem, the hoses are equipped with a connection means to suit the axial position of the electrode.
According to this embodiment the hoses are connected to a first connection assembly, which includes a plurality of elements connecting the hoses and is fixed solidly to the electrode-holder arm.
The adapter element of the electrode includes a second connection assembly, which is solidly fixed to the upper part of the adapter and mates with the first connection assembly and is connected to the cooling conduits located within the latter.
Both the connection assemblies include automatic closure means, which prevent the fluid contained therein from emerging from the hoses when the connection assemblies are disconnected.
When the electrode is lowered to its working position, the second connection assembly located on the electrode cooperates with the first connection assembly positioned on the electrode-holder arm, thus allowing the cooling fluid to circulate within the adapter.
Viceversa, when the electrode is raised to its inactive position, the two connection assemblies are disconnected and release the electrode.
This embodiment makes possible a ready dismantling of the electrode for carrying out maintenance and replacement of the graphite segment but does not make possible the adjustment of the axial position of the electrode inasmuch as every displacement of the electrode causes disengagement of the connection assemblies from each other and the resulting interruption of the circulation of cooling fluid.
EP-A-0167485 shows a device, substantially of the type described above, which serves to assist and accelerate the connection of the cooling water hoses after every replacement of the electrode.
This device comprises a connection assembly which is attached stationary to the electrode-holder arm; the assembly is connected on one side to the hoses which deliver the cooling water and on the other side includes apertures for the insertion of conduits for the supply of water, these conduits being connected to the adapter of the electrode.
There is also included a guide element, attached to the adapter, by means of which the conduits for the supply of water are guided inside the connection assembly, during the step of positioning the new electrode, until the conduits are connected with the delivery hoses.
This embodiment, if it does on the one hand assist the operations of connecting the various elements every time the electrode is changed, does not allow the electrode to be vertically moved, once the connections have been made, so as to adjust the length of the electrodes in the course of the melting process inside the furnace.
This is because the connection assembly is fixed on the electrode-holder arm and therefore cannot move with the electrode and follow its vertical movements of adjustment.